Classic fingerprint evidence remains a primary forensic method of identification in many criminal cases. Techniques are known for detecting fingerprints on a variety of materials, but they generally rely on either visible deposits or hidden (latent) fingerprints resulting from the transfer of residues from the finger to the surface.
Microscopic imaging techniques for this purpose suffer from severe limitations of scan area and scan speed. For example, atomic force microscopy can discern fingerprint residue on glass, but the scan area is restricted to 40 μm×40 μm, insufficient to image a whole fingerprint. Scanning electrochemical microscopy has a somewhat larger, but still restricted, scan area of 5 mm×3 mm; however, the scan time is 5 hours and significant sample preparation is required. Scanning Kelvin probe microscopy for latent fingerprint imaging is non-destructive and preserves DNA material, but is applicable to conducting surfaces only. The scan area and scan speed achieved are sufficiently large to allow a whole fingerprint image to be built up, but the scan time is relatively long, between 6 and 30 hours.
In addition, it is extremely difficult using conventional techniques to establish from fingerprint evidence alone even an approximate timeline of events, in terms of the length of time which has elapsed since the deposition of a fingerprint. Techniques for determining the time elapsed since deposition are generally based on one at least of: physical appearance; the effects of environmental factors; and chemical changes in the constituents of latent fingerprints. The first two methods suffer from the difficulty of reproducing the original conditions and hence of establishing what changes have occurred since the original event. The third is considered to be the most viable candidate practically, but latent prints are affected by a wide variety of factors, including subject factors and transfer and storage conditions. Subject factors include, for example, stress, metabolism, diet, health, age, sex, occupation and quantity and quality of finger contamination, all of which need to be taken into consideration. Transfer conditions include surface texture, physio-chemical structure, curvature, temperature, temperature difference, pressure and contact time. Storage environment parameters that are relevant include temperature, humidity, UV radiation, dust precipitation, condensation, friction, air circulation and atmospheric contamination.
Accordingly, the known techniques suffer from a variety of disadvantages, including cumbersome technology, the need for complex processing to factor in all of the possible variables, and the difficulty of achieving accurate measurements and/or evaluation.